Bone defects can be treated by the implantation of an autograft, an allograft, or a xenograft in the healing site. However, these biological implants suffer of many drawbacks, among them, for example, shortage of donor tissue, bacterial and viral contamination, etc. Biocompatible synthetic implants may present a safe and effective alternative for many indications.
In dental treatment, for example, the extraction of a tooth leaves an open wound that might be contaminated by bacteria. Moreover, it is a known problem, that due to the absence of the tooth, alveolar bone spontaneously undergoes remodeling, leading to its atrophy. Such atrophy may then cause many complications for subsequent reconstruction. In order to prevent this process, it has been suggested to implant into the extraction site a biocompatible, biodegradable open porous implant, which is configured and dimensioned to fit inside the tooth extraction socket. Unfortunately, the process of bone tissue regeneration competes with faster-growing soft tissue and epithelial cells, which tend to fill the bone repair site before sufficient bone growth is induced even when a osteoconductive scaffold is present.
To overcome this problem it is known from the prior art to employ a barrier material which is applied over the implant to exclude competitive cells and to avoid the migration of microscopic materials. This process is known as guided bone regeneration and involves a surgical placement and insertion of a barrier membrane which prohibits the in-growth of soft tissue and epithelial cells. Usually, after the initial surgical procedure, a removal of the membrane is necessary in order to avoid later inflammation and infection. There are also known biodegradable membranes which obviate the need for a subsequent removal operation. Nevertheless, these membranes are difficult to handle and implant. The surgical process is time consuming, cumbersome to the patient and involves considerably high costs.
In order avoid the drawbacks of the known prior art treatments with surgically placed membranes in WO 00/35510 it is suggested to provide the osteogenic bone graft with a zone of impermeability to soft tissue. The osteogenic bone graft comprises a coherent mass of bone particles from porcine or bovine bone. The zone of impermeability is obtained by reducing the porosity of a portion of the surface of the bone osteogenic graft This is achieved, e.g., by heating a portion of the surface area of the coherent bone mass, by crosslinking a portion of the surface area of the coherent bone mass and/or by applying one or more biocompatible masses to a portion of the surface area of the coherent bone mass to provide a microporous layer thereon and by combinations of the processes. By this treatment the zone of impermeability is formed as an integral, indivisibly interconnected portion of the osteogenic bone graft so as to form a single, unified whole which distinguishes from bone grafts which are combined with a separate barrier membrane material.
While the osteogenic bone grafts of WO 00/35510 avoid the drawbacks of prior art bone grafts which may be or may not be combined with surgically placed barrier membranes they too suffer from drawbacks. The base material for the bone particles usually is a natural, organically obtained porcine or bovine bone with all naturally occurring inadequaties. The obtaining of the bone particles from bones of organisms necessitates careful purification steps in order to avoid organic and genetic impurities. The production process may also require demineralization procedures to ensure that the inorganic mineral content is reduced to the required extent to obtain the desired porosity. These procedures are time consuming, cumbersome and involve considerable apparative and laborious efforts. The resultant product, thus, is rather scarce and costly. Moreover, the bone grafts from bone particles degrade very slowly and are rather incorporated in the host bone tissue.
While the problems of the prior art have been described with reference to dental problems it will be appreciated by those skilled in the art that implants are also used as treatments for other skeleton parts. If, for example, a part of the skeleton is stricken by a tumor, the area stricken by the tumor may be removed and replaced by an implant. In that case with the implants known from the prior art similar problems as those described with respect to dental treatments may arise.